This invention relates generally to the art of moulding plastic articles and is concerned more particularly with an apparatus for handling the plastic articles after moulding. An apparatus of this type is referred to in the art as a xe2x80x9ctake-outxe2x80x9d system.
The invention is concerned in particular with a take-out system for shuttle-type plastic blow moulding machines. In a shuttle-type blow moulding machine, at least one tubular parison is continuously extruded between two blow moulding assemblies, each of which includes a pair of separable mould parts. The assemblies alternately xe2x80x9cshuttlexe2x80x9d back and forth between respective moulding positions and a position in which the mould parts close around and severe a portion of the parison from the upstream portion of the parison that is being continuously extruded. The moulding assembly then returns to its moulding position and air is applied to expand the severed portion of the parison into the mould. The mould then opens. A take-out systems is used to remove the moulded articles and deliver them to a discharge position, e.g. on a discharge conveyor. At the time the moulds open, the plastic articles are formed but not completely xe2x80x9cfrozenxe2x80x9d in their final shape. Accordingly, the take-out system must be designed to handle the articles without distorting their shape.
Prior art take-out systems for shuttle-type blow moulding machines typically have two separate gripper heads, each positioned below one of the blow moulding assemblies. The individual gripper heads move up and down in synchronism with the release of moulded articles from the moulding assemblies. In an upper position, each head grips the moulded article or articles released from the particular moulding assembly and then moves down to a release position. Typically, a common conveyor mechanism is provided at the release position for receiving and transporting laterally the articles taken out by the two gripper heads. Since the moulding assemblies operate alternately and the gripper heads accordingly must move up and down alternately, the conveyor mechanism must xe2x80x9cwaitxe2x80x9d until the plastic articles from both gripper heads have been delivered, before the batch of articles can be discharged. In an alternative version of the machine, separate take-off conveyors can be provided for each gripper head, but the conveyors then discharge in opposite directions and the two groups of articles must be brought together downstream, for subsequent handling. There are a number of disadvantages associated with prior art take-out systems. One is that two separate gripper heads and associated actuating equipment is required. Another is that the systems tend to be designed using actuators that move through fixed distances (e.g. air cylinders) so that there is limited adjustability. This means that the systems tend to be quite difficult to set up and require the services of a skilled technician. Also, the systems usually are designed for use with particular types of blow moulding machines and cannot easily be adapted for use with different machines. By way of example, the center-to-center distance between the two moulding assemblies can vary widely from one machine to another. A typical range might be 29xe2x80x3 to 40xe2x80x3 center-to-center.
An object of the present invention is to provide an improved take-out apparatus that is designed to address these disadvantages of the prior art.
It will be understood that, as compared with prior art take-out systems, the method of the invention has a number of advantages. First, there is only one gripper head for taking out moulded articles from both moulding assemblies. Further, since the drive means associated for achieving movement in the first and second direction may be infinitely variable, so that there is infinite versatility to control the motion of the gripper head. This means that it is possible to xe2x80x9cprogramxe2x80x9d the motion of the gripper head as appropriate to the particular application, and that the apparatus as a whole can be adjusted to fit different positions of the moulding assemblies that might be found in different moulding machines.
According to a particular preferred embodiment the drive means for the carriage on the first linear guide may, comprise an endless belt to which the carriage is coupled, and an electric servomotor for reciprocating the belt. Similarly, an electric servomotor may be used to drive a rack and pinion arrangement which includes a vertically adjustable arm, for infinitely varying the vertical displacement of the gripper head. The use of electric servomotors in turn allows for computer control of the apparatus. For example, by using appropriately designed software, the motion of the carriage along the first linear guide means and the gripper head on the second linear guide means may be automatically controlled from a computer terminal.
The software can be designed to allow the operator to simply input co-ordinates or distances to program the motion of the gripper head. For example, the carriage will be required to alternately move different linear distances along the first guide means to position the gripper head between the two moulding assemblies of the moulding machine. In order to achieve as short a cycle time as possible, it may be desirable to program the drive means so that they both operate at the same time and move the gripper head in an arcuate path in travelling between the two article engaging positions below the mould assemblies and the release position. Different release positions can be provided for articles from the respective moulding assemblies.
In summary, the use of infinitely variable drive means, coupled with appropriate software control can provide the operator with complete freedom to program all aspects of the motion of the gripper head.
The method of the invention may also include trimming excess plastic material from the moulded article prior to discharge.